1. Field of the Invention
The present invention relates to a mixture of alkylated diphenylamines, to a process for the preparation of that mixture, and to the use thereof as an additive for stabilizing organic products that are subjected to oxidative, thermal, and/or light-induced degradation. The additives can be added to numerous organic products widely used in engineering, for example, lubricants, hydraulic fluids, metal-working fluids, fuels, or polymers, to improve their performance properties.
2. Description of Related Art
U.S. Pat. No. 2,943,112 describes anti-oxidants from the group of the alkylated diphenylamines that are prepared by reaction of diphenylamine with alkenes in the presence of mineral acids and large quantities of acid clays as catalysts. Alkylation of the diphenylamine with alkenes results in mixtures of mono- and di-alkylated diphenylamine. In that process, relatively large quantities of the starting material, generally from 6 to 12% diphenylamine, are not reacted, which reduces the anti-oxidative efficacy of the alkylated diphenylamines, leads to the deposition of sludge, and imparts undesirable toxic properties to the product. Reaction with additional alkenes is proposed as an alternative to the distillative separation of the starting material from the products.
U.S. Pat. No. 3,496,230 describes the preparation of a mixture of 80% dinonyldiphenylamine and 15% nonyldiphenylamine in the presence of Friedel-Crafts catalysts of the aluminum chloride type, but that mixture still has a diphenylamine content of 2% (see Example 2 of the patent). As has been shown in U.S. Pat. No. 6,315,925, the preparation of that mixture is especially disadvantageous since it is contaminated by traces of chlorine, metal compounds, and undesirable by-products, e.g. N-alkylated diphenylamines and diphenylamines alkylated in the 2- and 2′-positions, is black in color, and is very viscous.
U.S. Pat. No. 4,824,601 discloses a process for the production of a liquid antioxidant composition by reaction of diphenylamine with diisobutylene comprising reacting diphenylamine with diisobutylene in a molar ratio of from 1:1.1 to 1:2.5 and in the presence of an acid activated earth catalyst, while ensuring that the concentration of diisobutylene remains substantially constant throughout the reaction period at a reaction temperature of at least 160° C., the reaction being effected for such a period that the content of 4,4′-dioctyldiphenylamine in the reaction mass, excluding catalyst, is below 25% by weight; and removing catalyst and unreacted diisobutylene. The use of this product as a stabilizer for organic material against oxidative degradation is also disclosed.
U.S. Pat. No. 6,315,925 discloses a mixture of nonylated diphenylamines, especially dinonylated diphenylamines, and a technically advantageous methodological process for the preparation of that mixture by using acid catalysts in small quantities. The mixture is used as an additive for stabilizing organic products that are subjected to oxidative, thermal, and/or light-induced degradation.
U.S. Pat. No. 6,355,839 discloses a process for the preparation of alkylated diphenylamine antioxidants that comprises alkylating diphenylamine with a polyisobutylene in the presence of a clay catalyst, wherein the polyisobutylene has an average molecular weight in the range of 120 to 600 and wherein the polyisobutylene contains at least 25% methylvinylidene isomer.
The disclosures of the foregoing are incorporated herein by reference in their entirety.